Techniques for tracking exhaust gas constituents through a low pressure exhaust gas recirculation system of a turbocharged gasoline engine

ABSTRACT

Systems and methods for a turbocharged gasoline engine utilize an exhaust gas concentration sensor disposed upstream from an exhaust gas recirculation pickup point of a low pressure EGR (LPEGR) system of the engine and a controller configured to receive a measured air/fuel ratio of the exhaust gas from the sensor, determine an air/fuel ratio of the exhaust gas at the EGR pickup point, determine an air/fuel ratio of the exhaust gas at an inlet and outlet of an EGR cooler, determine first/second sets of exhaust gas fractions and fuel fractions upstream/downstream from an EGR port that is upstream from a compressor in an induction system of the engine, and control at least one of a wastegate valve, a throttle valve, a fuel injector, and a spark plug based on the sets of second exhaust gas fractions and fuel fractions to prevent misfires of the engine.

FIELD

The present application generally relates to exhaust gas recirculation(EGR) and, more particularly, to techniques for tracking exhaust gasconstituents through a low pressure EGR (LPEGR) system of a turbochargedgasoline engine.

BACKGROUND

A turbocharged engine utilizes a compressor of a turbocharger to forceair through an induction system and a throttle valve and into an intakemanifold. The air is combined with fuel and combusted within cylinders,and exhaust gas resulting from combustion is expelled from the cylindersinto an exhaust system. The kinetic energy of the exhaust gas drives aturbine of the turbocharger, which in turn drives the compressor. Theengine could also include a low pressure exhaust gas recirculation(LPEGR) syste that recirculates exhaust gas from downstream of theturbine and a catalytic converter to upstream of the compressor. Theportion of recirculated exhaust gas is regulated by an EGR valve. TheEGR and throttle valves require accurate, coordinated control. Thistypically requires a large quantity of sensors, which is expensive.Accordingly, while such turbocharged engine systems work ell for theirintended purpose, there remains a need for improvement in the relevantart.

SUMMARY

According to one example aspect of the invention, a control system for avehicle including a gasoline engine, a turbocharger comprising awastegate valve, and a low pressure exhaust gas recirculation (LPEGR)system, the LPEGR system comprising an EGR cooler and an EGR valvedownstream from the EGR cooler, the LPEGR system being configured torecirculate exhaust gas produced by the engine from an exhaust system ofthe engine to an induction system of the engine, is presented. In oneexemplary implementation, the control system comprises: a throttle valvedisposed in the induction system between a compressor of theturbocharger and an intake port of a cylinder of the engine andconfigured to control airflow into the engine; a fuel injectorconfigured to inject gasoline into the cylinder; a spark plug configuredto generate a spark to ignite a mixture of gas and the gasoline withinthe cylinder; an exhaust gas concentration sensor upstream from an EGRpickup of the LPEGR system and configured to measure an air/fuel ratioof the exhaust gas; and a controller configured to: receive a measuredair/fuel ratio of the exhaust gas from the exhaust gas concentrationsensor; determine an air/fuel ratio of the exhaust gas at the EGR pickuppoint; determine an air/fuel ratio of the exhaust gas at an inlet of theEGR cooler; determine an air/fuel ratio of the exhaust gas at an outletof the EGR cooler; determine a first exhaust gas fraction and a firstfuel fraction at an EGR port upstream from the compressor in theinduction system where the exhaust gas mixes with air; determine a setof second exhaust gas fractions and second fuel fractions at a set ofrespective points in the induction system downstream from the EGR port;and control at least one of the wastegate valve, the throttle valve, thefuel injector, and the spark plug based on the set of second exhaust gasfractions and second fuel fractions to prevent misfires of the engine.

In some implementations, the controller is configured to control thewastegate valve based on a determined second exhaust gas fraction and adetermined second fuel fraction at an inlet of the compressor. In someimplementations, the controller is configured to control the throttlevalve based on a determined second exhaust gas fraction and a determinedsecond fuel fraction at an inlet of the throttle valve. In someimplementations, the controller is configured to control the fuelinjector and the spark plug based on a determined second exhaust gasfraction and a determined second exhaust gas fraction at the cylinderintake port. In some implementations, the controller is furtherconfigured to utilize the determined second exhaust gas fraction and thedetermined second exhaust gas fraction at the cylinder intake port aspart of an EGR condition check upon shutdown and restart of the engine.

In some implementations, the induction system further comprises adifferential pressure (dP) valve disposed upstream of the EGR port anddownstream from an air filter of the induction system. In someimplementations, the controller determines the exhaust gas fraction andfuel fraction at the EGR mixing point based on the operation of the dPvalve. In some implementations, the controller is configured to divide aflow path of the exhaust gas through the LPEGR system and the inductionsystem into the following distinct portions: (i) a first portion fromthe exhaust gas concentration sensor to the EGR pickup point; (ii) asecond portion from the EGR pickup point to the EGR cooler inlet; (iii)a third portion from the EGR cooler inlet across the EGR cooler to theEGR cooler outlet; (iv) a fourth portion from the EGR cooler outletacross the EGR valve to the EGR port; (v) a fifth portion from the EGRport to the compressor inlet; (vi) a sixth portion from an outlet of thecompressor to an inlet of a cold air cooler of the induction system;(vii) a seventh portion across the cold air cooler; (viii) an eighthportion from an outlet of the cold air cooler to an inlet of thethrottle valve; and (ix) a ninth portion from an outlet of the throttlevalve across an intake manifold of the induction system to the cylinderintake port.

In some implementations, the controller utilizes predeterminedinformation about the configuration of the LPEGR system and theinduction system and distinct memory buffers to track (i) the air/fuelratio of the exhaust gas between the nine distinct portions of the flowpath before EGR mixing and (ii) EGR/fuel fractions between the ninedistinct potions of the flow path after EGR mixing. In someimplementations, the controller is configured to vary air/fuel ratiodata or EGR/fuel fraction data stored in each memory buffer to accountfor (i) mass changes at the EGR pickup point and the EGR port, (ii)density changes in across the EGR cooler, the compressor, the cold aircooler, and the throttle valve, and (iii) dynamic flows from an outletof the compressor to the inlet of the cold air cooler and from an outletof the throttle valve to the cylinder intake port.

According to another example aspect of the invention, a method fortracking exhaust gas constituents for a vehicle including an enginehaving a turbocharger with a wastegate valve, a throttle valve disposedin an induction system between a compressor of the turbocharger and anintake port of a cylinder, a fuel injector configured to inject gasolineinto the cylinder, and a spark configured to generate spark within thecylinder, the vehicle further including a low pressure exhaust gasrecirculation (LPEGR) system having an EGR cooler and an EGR valve andbeing configured to recirculate exhaust gas produced by the engine froman exhaust system to the induction system, is presented. In oneexemplary implementation, the method comprises: receiving, by acontroller and from an exhaust gas concentration sensor upstream from anEGR pickup point of the LPEGR system, a measured air/fuel ratio of theexhaust gas; determining, by the controller, an air/fuel ratio of theexhaust gas at the EGR pickup point; determining, by the controller, anair/fuel ratio of the exhaust gas at an inlet of the EGR cooler;determining, by the controller, an air/fuel ratio of the exhaust gas atan outlet of the EGR cooler; determining, by the controller, a firstexhaust gas fraction and a first fuel fraction at an EGR port upstreamfrom the compressor in the induction system where the exhaust gas mixeswith air; determining, by the controller, a set of second exhaust gasfractions and second fuel fractions at a set of respective points in theinduction system downstream from the EGR port; and controlling, by thecontroller, at least one of the wastegate valve, the throttle valve, thefuel injector, and the spark plug based on the set of second exhaust gasfractions and second fuel fractions to prevent misfires of the engine.

In some implementations, the method further comprises controlling, bythe controller, the wastegate valve based on a determined second exhaustgas fraction and a determined second fuel fraction at an inlet of thecompressor. In some implementations, the method further comprisescontrolling, by the controller, the throttle valve based on a determinedsecond exhaust gas fraction and a determined second fuel fraction at aninlet of the throttle valve. In some implementations, the method furthercomprises controlling, by the controller, the fuel injector and thespark plug based on a determined second exhaust gas fraction and adetermined second exhaust gas fraction at the cylinder intake port. Insome implementations, the method further comprises utilizing, by thecontroller, the determined second exhaust gas fraction and thedetermined second exhaust gas fraction at the cylinder intake port aspart of an EGR condition check upon shutdown and restart of the engine.

In some implementations, the induction system further comprises adifferential pressure (dP) valve disposed upstream of the EGR port anddownstream from an air filter of the induction system. In someimplementations, the method further comprises determining, by thecontroller, the exhaust gas fraction and fuel fraction at the EGR mixingpoint based on the operation of the dP valve. In some implementations,the method further comprises dividing, by the controller, a flow path ofthe exhaust gas through the LPEGR system and the induction system intothe following distinct portions: (i) a first portion from the exhaustgas concentration sensor to the EGR pickup point; (ii) a second portionfrom the EGR pickup point to the EGR cooler inlet; (iii) a third portionfrom the EGR cooler inlet across the EGR cooler to the EGR cooleroutlet; (iv) a fourth portion from the EGR cooler outlet across the EGRvalve to the EGR port; (v) a fifth portion from the EGR port to thecompressor inlet; (vi) a sixth portion from an outlet of the compressorto an inlet of a cold air cooler of the induction system; (vii) aseventh portion across the cold air cooler; (viii) an eighth portionfrom an outlet of the cold air cooler to an inlet of the throttle valve;and (ix) a ninth portion from an outlet of the throttle valve across anintake manifold of the induction system to the cylinder intake port.

In some implementations, the method further comprises utilizing, by thecontroller, predetermined information about the configuration of theLPEGR system and the induction system and distinct memory buffers totrack (i) the air/fuel ratio of the exhaust gas between the ninedistinct portions of the flow path before EGR mixing and (ii) theEGR/fuel fractions between the nine distinct portions of the flow pathafter EGR mixing. In some implementations, the method further comprisesvarying, by the controller, air/fuel ratio data or the EGR/fuel fractiondata stored in each memory buffer to account for (i) mass changes at theEGR pickup point and the EGR port, (ii) density changes in across theEGR cooler, the compressor, the cold air cooler, and the throttle valve,and (iii) dynamic flows from an outlet of the compressor to the inlet ofthe cold air cooler and from an outlet of the throttle valve to thecylinder intake port.

Further areas of applicability of the teachings of the presentdisclosure will become apparent from the detailed description, claimsand the drawings provided hereinafter, wherein like reference numeralsrefer to like features throughout the several views of the drawings. Itshould be understood that the detailed description, including disclosedembodiments and drawings referenced therein, are merely exemplary innature intended for purposes of illustration only and are not intendedto limit the scope of the present disclosure, its application or uses.Thus, variations that do not depart from the gist of the presentdisclosure are intended to be within the scope of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example vehicle according to the principles ofthe present disclosure;

FIG. 2 is a flow diagram of an example engine control method accordingto the principles of the present disclosure;

FIGS. 3A-3C are functional block diagrams of example exhaust gasrecirculation (EGR) valve control, differential pressure (dP) valvecontrol, and EGR valve mass flow and EGR/fuel fraction estimationarchitectures of a controller of the vehicle according to the principlesof the present disclosure;

FIG. 4 is a flow diagram of an example EGR valve and dP valve controlmethod according to the principles of the present disclosure;

FIGS. 5A-5F are functional block diagrams of example gas pressureadaptation architectures of the controller of the vehicle according tothe principles of the present disclosure;

FIGS. 6A-6B are flow diagrams of example gas pressure adaptation methodsaccording to the principles of the present disclosure;

FIGS. 7A-7D are diagrams of example exhaust gas constituent trackingfeatures according to the principles of the present disclosure; and

FIG. 8 is a flow diagram of an example method of tracking exhaust gasconstituents through a low pressure EGR (LPEGR) and an induction systemof a turbocharged engine of a vehicle according to the principles of thepresent disclosure.

DETAILED DESCRIPTION

As previously discussed, low pressure exhaust gas recirculation (LPEGR)systems comprise an EGR valve that must be precisely controlled inconjunction with a throttle valve of an engine. These LPEGR systemsrecirculate low pressure exhaust gas from a point downstream from aturbine and a catalytic converter. In contrast to traditional highpressure EGR systems, a minor fluctuation of a few kilopascals (kPa)could cause significant changes in EGR flow, EGR control error, andnoise/vibration/harshness (NVH) in an LPEGR system. While conventionaldiesel engines often utilize LPEGR systems, diesel engines controltorque output via fuel control. Compression ignition of air and dieselfuel is also entirely different than spark ignition of air and gasolinefuel. Diesel engines, for example, utilize EGR for nitrogen oxide (NOx)reduction, whereas gasoline engines utilize EGR for pumping loss andknock/auto-ignition reduction. Also, diesel engines are always lean burnand have a much wider air/fuel ratio (FAR) range, so the EGR accuracyfor diesel engines is less critical. Gasoline engines, on the otherhand, require a precise FAR for the combustible air/fuel mixture (e.g.,within a very precise range). In addition, gasoline engines require thatthe FAR of the exhaust gas is at stoichiometric so that a three-waycatalytic converter is able to achieve its best emission conversionefficiency. For at least these reasons, the EGR fraction control andestimation is critical for gasoline engines. Inaccurate EGR control andestimation could cause a significant reduction in fuel economy andpotential significant engine hardware failure.

Aside from the hardware differences between high pressure EGR (HPEGR)and LPEGR systems, the engine operation conditions between the two arealso different. HPEGR is used under low load to mid load conditionsbecause the EGR valve upstream pressure (exhaust pressure) is higherthan the intake manifold pressure, so there is enough differentialpressure across the EGR valve to drive EGR into the intake manifold.However, under full/high load conditions and for boosted applications,the intake manifold pressure is too high for EGR to be forced into it.As mentioned above, LPEGR is somewhat common for diesel engines because(i) diesel engines run under boost conditions most of the time, (ii)there is no need to HPEGR under low load conditions (no pumping lossreduction necessary), and (iii) the EGR control and estimation accuracyrequirement is low or nonexistent. LPEGR is uncommon or unpopular ongasoline engines, on the other hand, because (i) naturally aspiratedengines don't require LPEGR, (ii) LPEGR control accuracy is difficult toachieve, (iii) there are potential NVH issues (exhaust noise deliveredinto the induction system, as described above), and (iv) it is difficultto deliver enough EGR to the intake manifold under low load to mid loadengine operating conditions.

Utilizing sensors throughout the LPEGR system would allow for moreaccurate control, but implementing additional sensors increases costs.Conventional pressure models are also not adaptable in that they areable to adjust themselves over time (e.g., due to component aging,part-to-part variability, changes due to ambient conditions, etc.).Additionally, because the flow path of the LPEGR system is much longerthan a high pressure EGR system, there is a substantial delay betweencontrolling the EGR valve to when the recirculated exhaust gas reachesthe intake port of the engine. For example, a high pressure EGR systemcould include a short flow path from the exhaust manifold to the intakemanifold, whereas the LPEGR system may have a very long flow path fromdownstream of a catalytic converter all the way back to further upstreamin the induction system (e.g., before a compressor). Thus, the exhaustgas constituents (inert gas (the combusted mixture, e.g., CO2 and H2O),hydrocarbons, etc.) must be accurately tracked throughout the flow path.It is less critical for high pressure EGR systems to accurately trackexhaust gas constituents because of their much shorter flow path.Similarly, diesel engines do not need to accurately track exhaust gasconstituents because these are primarily utilized for spark control,which does not occur in diesel engines. Utilizing a plurality of exhaustgas concentration sensors throughout the flow path would allow foraccurate monitoring, but these sensors are expensive. In addition,transient response and accuracy under dynamic pressure conditions areissues for wide-range oxygen (WRO2) sensors, which are used to monitorEGR concentrations throughout the flow path.

Accordingly, an improved control system for a turbocharged gasolineengine with an LPEGR system is presented. A differential pressure (dP)valve is implemented downstream of an air filter and upstream from thecompressor and the LPEGR port. This dP valve is controlled to maintainenough differential pressure across the EGR valve to deliver a desiredEGR mass flow under a wide range of engine operating conditions. Anotherbenefit of the dP sensor is mitigating or eliminating the NVH that couldoccur in LPEGR systems as the EGR path can be construed to be an exhaustleak when EGR is flowing and hence can attenuate exhaust noise outthrough the induction system (e.g., through an airbox). Only threepressure sensors and one exhaust gas concentration sensor are requiredby the LPEGR control system: a dP valve outlet pressure sensor, an EGRvalve delta pressure sensor, a barometric pressure sensor, and anexhaust gas concentration sensor (e.g., a WRO2 sensor in the exhaust)associated with the LPEGR system. Other important pressures are modeledand short term and/or long term adaptation is applied to variousmeasured/modeled pressures (to account for catalytic converter aging,air filter clogging, etc.). The exhaust gas constituents are alsotracked through the LPEGR flow path and utilized for engine control.More particularly, when the EGR valve is closed, there is still exhaustgas flowing through the induction side of the LPEGR path, and byaccurately tracking the exhaust gas constituents, fuel and spark of theengine are precisely controlled, e.g., to avoid potential misfires.Long-term sensor adaptation, e.g., of the exhaust WRO2 sensor, alsoimproves trapped air flow and torque estimation and open-loop air/fuelratio delivery.

Referring now to FIG. 1, an example engine system 101 for a vehicle orvehicle powertrain 100 is illustrated. The engine system 101 includes agasoline engine 102 that receives air from an induction system 104. Aninduction path 106 receives fresh air that is filtered by an air filter(AF) 108. A dP valve 110 regulates the flow of air through the inductionpath 106 and a pressure in induction paths 112 a, 112 b. Turbochargers114 a, 114 b comprise compressors 116 a, 116 b (“compressors 116”) thatforce air/exhaust gas from the induction paths 112 a, 112 b throughinduction paths 118 a, 118 b that converge into a single induction path120. While two turbochargers 114 a and 114 b are shown, it will beappreciated that the engine system 101 could have only one turbocharger.A throttle valve 122 regulates the flow of air/exhaust gas through anoptional charge air cooler (CAC) 124 and into an intake manifold 126. Itwill be appreciated that the throttle 122 could be implementeddownstream from the CAC 124. The air/exhaust gas in the intake manifold126 is provided to a plurality of cylinders 128, combined with gasolinefrom fuel injectors 130 and combusted by spark from spark plugs 132 todrive pistons (not shown) that generate drive torque to propel thevehicle 100. While six cylinders are shown, it will be appreciated thatthe engine 102 could include any suitable number of cylinders.

Exhaust gas resulting from combustion is expelled from the cylinders 128into exhaust manifolds 134 a, 134 b. Each exhaust manifold 134 a, 134 b,for example, could be associated with three of the six cylinders 128.The exhaust gas in exhaust manifold 134 a flows through exhaust path 136a and its kinetic energy drives a turbine 138 a of turbocharger 114 a.The turbine 138 a drives compressor 116 a via a shaft 140 a. Similarly,the exhaust gas in exhaust manifold 134 b flows through exhaust path 136b and its kinetic energy drives a turbine 138 b of turbocharger 114 b,which in turn drives compressor 116 b via a shaft 140 b. Wastegatevalves 141 a, 141 b regulate turbocharger speed/boost pressure. Theexhaust gas flows from turbines 138 a, 138 b through exhaust paths 142a, 142 b and is treated by exhaust treatment systems (ETS) 144 a, 144 bto decrease or eliminate emissions before being released into theatmosphere. ETS 144 b is shown to include a three-way catalyticconverter (TWC) 145 and a muffler (MUF) 147. It will be appreciated thateach ETS 144 a, 144 b could include other exhaust treatment components.

An LPEGR system 146 recirculates exhaust gas from an EGR pickup pointbetween the catalytic converter 145 and the muffler 147 through an EGRpath 148 that is regulated by an EGR valve 150. The EGR path 148 splitsinto separate EGR paths 152 a, 152 b which direct the exhaust gas toports in induction paths 112 a, 112 b downstream of the dP valve 110 andupstream of the compressors 116 a, 116 b. The LPEGR system 146 includesan EGR cooler (EGRC) 154 that cools the exhaust gas. Becauseturbocharged gasoline engines operate at very high temperatures, coolingof the recirculated exhaust gas provides for increased performance. Acontroller 156 controls operation of the engine system 101. It will beappreciated that the term “controller” as used herein refers to anysuitable control device or set of multiple control devices that is/areconfigured to perform at least a portion of the techniques of thepresent disclosure. Non-limiting examples include anapplication-specific integrated circuit (ASIC) and one or moreprocessors and a non-transitory memory having instructions storedthereon that, when executed by the one or more processors cause thecontroller to perform a set of operations. The one or more processorscould be either a single processor or two or more processors operatingin a parallel or distributed architecture.

The controller 156 includes a barometric pressure sensor 158 thatmeasures barometric pressure. It will be appreciated that the barometricsensor 158 could be external to the controller 156. An EGR valve deltapressure sensor 160 is disposed proximate to the EGR valve 150 andmeasures a delta pressure across the EGR valve 150. A dP valve outletpressure sensor 162 measures a pressure at an outlet of the dP valve110. This dP valve outlet pressure also corresponds to inlet pressuresof the compressors 116 a, 116 b. Lastly, exhaust gas concentrationsensors 164 a, 164 b measure exhaust gas concentration. However, onlyexhaust gas concentration sensor 164 b is required for the techniques ofthe present disclosure because it is associated with the LPEGR system146. In one exemplary implementation, the exhaust gas concentrationsensors 164 a, 164 b are WRO2 sensors configured to measure an air/fuelratio (FA) of the exhaust gas. It will be appreciated that the enginesystem 101 could include other suitable sensors, such as an exhaust gasor back pressure sensor (not shown). All of these sensors provide theirmeasurements to the controller 156, e.g., via a controller area network(CAN).

EGR Valve and dP Valve Control

Referring now to FIGS. 3A-3C, functional block diagrams of example EGRvalve control, dP valve control, and EGR valve mass flow and EGR/fuelfraction estimation architectures are illustrated. In one exemplaryimplementation, these architectures are implemented in the controller156.

In FIG. 3A, an example EGR valve position control architecture 300 isillustrated. Block 302 determines a desired EGR (or burned gas) fractionfor the engine 102. Block 304 compensates the desired EGR fraction for anon-stoichiometric air/fuel ratio. Block 306 determines a target EGRmass flow. Blocks 308 and 310 model EGR valve inlet and outletpressures, respectively. The outputs of blocks 306, 308, and 310 are fedto block 312 that calculates a target effective flow area (CdA) for theEGR valve 150 based on a compressible flow method. Block 314 utilizes aone-dimensional surface to convert the calculated CdA to a target EGRvalve position. Closed-loop adjustment of the target EGR valve positionis performed based on a difference between the target EGR mass flow(from block 306) and an estimated EGR flow from block 316. Thisdifference output by block 318 is run through a proportional-integral(PI) controller 320 and the output is the adjustment to the target EGRvalve position at block 322.

In FIG. 3B, an example dP valve position control architecture 330 isillustrated. Differences are calculated between compressor and inductionsystem hardware pressure limits and measured barometric pressure (frombarometric pressure sensor 158) at blocks 332-340. Another difference iscalculated between the modeled EGR valve inlet pressure and a target EGRvalve delta pressure (e.g., to meet NVH goals or constraints) at blocks342-346. Each of these differences is fed to block 348, which outputsthe maximum of the three differences as a target dP valve outletpressure. As previously discussed herein, the target dP valve outletpressure is also the target compressor inlet pressure. Anotherdifference is calculated between the modeled air filter outlet pressureand the target dP valve outlet pressure at blocks 350-352. Thisdifference is a target dP valve delta pressure. The target dP valvedelta pressure is saturated at zero at block 354. Block 358 utilizes atwo-dimensional surface to determine a target dP valve position based onthe saturated target dP valve delta pressure and a current dP valve massflow (from block 356). Closed-loop adjustment of the target dP valveposition is performed based on a difference between a measured dP valveoutlet pressure from block 360 (measured by the dP valve outlet pressuresensor 162) and the target dP valve outlet pressure (from block 348).This difference output by block 362 is run through aproportional-integral (PI) controller 364 and the output is theadjustment to the target dP valve position at block 366. Additionally,when the target dP valve delta pressure falls below zero, a reset signalfor the PI controller block 364 (e.g., reset to zero) is generated byblock 368.

In FIG. 3C, an example EGR valve mass flow and EGR/fuel fractionestimation architecture 370 is illustrated. Block 372 outputs thecurrent EGR valve position. Block 374 utilizes one-dimensional surfaceto convert the current EGR valve position to a current effective flowarea (CdA) for the EGR valve 150. Block 376 receives the output of block374, the measured EGR valve delta pressure (measured by the EGR valvedelta pressure sensor 160) from block 378, and the measured dP valveoutlet pressure (measured by the dP valve outlet pressure sensor 162)from block 380. Block 376 performs a compressible flow based estimationof the current EGR valve mass flow. Block 382 receives the output ofblock 376 and estimates the current EGR valve mass flow rate. The outputof block 382 and a measured exhaust gas (e.g., 02) concentration(measured by exhaust gas concentration sensor 164 b) from block 384 arefed to an EGR transport delay model block 386. Block 386 utilizes an EGRtransport delay model, which models the flow of EGR through the LPEGRsystem 146 and takes into account the associated delay, along with theother inputs to model each of a compressor inlet EGR fraction (block388), a throttle valve inlet EGR fraction (block 390), an intake portEGR fraction (block 392), and an intake port fuel fraction (block 394).Each of these modeled parameters is then utilized in controllingoperation of the engine 102 (e.g., fuel and/or spark).

Referring now to FIG. 4, a flow diagram of an example method 400 ofcontrolling the EGR valve 150 and the dP valve 110 is illustrated. At404, the controller 156 receives a set of measured pressures. In oneexemplary implementation, these measured pressures include EGR valvedelta pressure, dP valve outlet pressure, and barometric pressure. From408, the method 400 splits into two coordinated control loops, one foreach of the EGR valve 150 and the dP valve 110. At 408, the controller156 determines the target EGR valve mass flow. At 412, the controller156 models the EGR valve inlet/outlet pressures based on the target EGRvalve mass flow and the measured EGR valve delta pressure. At 416, thecontroller 156 estimates an open-loop EGR valve position based on thetarget EGR mass flow and the modeled EGR valve inlet/outlet pressures.At 420, the controller 156 determines the target EGR valve positionbased on the estimated open-loop EGR valve position. At 424, thecontroller 156 controls the EGR valve 150 based on the target EGR valveposition. This includes closed-loop adjustment of the target EGR valveposition at 432 based on a difference or error between the target EGRvalve mass flow and the estimated EGR valve mass flow, which is comparedto a threshold at 428. When the error satisfies the threshold, themethod 400 ends or returns to 404. At 436, the controller 156 determinesthe target dP valve outlet pressure. At 440, the controller 156determines the target dP valve delta pressure based on the target dPvalve outlet pressure. At 444, the controller 156 determines the targetdP valve position based on the target dP valve delta pressure. At 448,the controller 156 controls the dP valve 110 based on the target dPvalve position. This includes closed-loop adjustment of the target dPvalve position at 456 based on a difference or error between themeasured dP valve outlet pressure and the target dP valve outletpressure, which is compared to a threshold at 452. When the errorsatisfies the threshold, the method 400 ends or returns to 404.

Gas Pressure Adaptation

Referring now to FIGS. 5A-5F, functional block diagrams of example gaspressure adaptation architectures are illustrated. In one exemplaryimplementation, these architectures are implemented in the controller156.

FIG. 5A illustrates a high-level gas pressure adaptation architecture500. This architecture includes both long term and short termadaptations. The long term adaptations involve accumulating errorthroughout a life of the vehicle to determine a multiplier that isutilized for correction. For example, the catalytic converter 152 agesover time, which affects exhaust gas pressure. Similarly, for example,the air filter 108 fills or clogs with filtered matter, which affectsinduction air pressure. Short term adaptation, on the other hand, isperformed for points that are directly associated with a sensor and thusare able to be adjusted in the short term based on sensor feedback. AnEGR pickup pressure long term adaptation block 501 and an EGR coolerpressure loss long term adaptation block 502 each receive both themeasured dP valve outlet pressure (from sensor 162) and the measured EGRvalve delta pressure (from sensor 160). An air filter pressure loss longterm adaptation block 503 only receives the measured dP valve outletpressure. An EGR valve inlet pressure short term adaptation block 504receives both the measured dP valve outlet pressure and the EGR valvedelta pressure. A dP valve outlet pressure short term adaptation block505 only receives the measured dP valve outlet pressure.

Block 501 calculates and outputs an EGR pickup pressure multiplier. Thismultiplier is applied to an EGR pickup pressure loss obtained from acalibrated EGR pickup pressure to barometric pressure loss table 506 toobtain the modeled EGR pickup pressure. Block 502 calculates and outputsan EGR cooler pressure multiplier. This multiplier is applied to an EGRcooler pressure loss obtained from a calibrated EGR cooler pressure losstable 507 to obtain the modeled EGR cooler outlet pressure. Block 504calculates and outputs a short term correction for the EGR valve inletpressure, which is summed with the modeled EGR cooler outlet pressureloss and the modeled EGR pickup pressure loss at block 508 to obtain themodeled EGR valve inlet pressure. Modeled EGR valve outlet pressure isthen obtained from the modeled EGR valve inlet pressure using themeasured EGR valve delta pressure. Block 503 calculates and outputs anair filter pressure multiplier. This multiplier is applied to an airfilter pressure loss obtained from a calibrated air filter pressure losstable 509 to obtain the modeled air filter outlet pressure. Block 505calculates and outputs a short term correction for the dP valve outletpressure. A calibrated dP valve pressure loss surface 510 is utilized toobtain a dP valve pressure loss. The outputs of blocks 504, 505, and 510are summed at block 511 to obtain the modeled dP valve outlet pressure.

FIG. 5B illustrates an example architecture 520 for the EGR pickuppressure long term adaptation block 501. The architecture 520 isgenerally divided into enable conditions block 521 and the actual EGRpickup long term adaption block 522. The enable conditions 521 blockincludes EGR mass flow being below a certain threshold at block 523, theexhaust mass flow being stable (e.g., remaining within a certain range)at block 524, the EGR valve delta pressure and dP valve outlet pressuresensors 160, 162 being ready for measurement (e.g., nofaults/malfunctions) at block 525, and the EGR pickup pressure learncomplete flag being false (e.g., a learn has not already been performedor the modeled pressure is larger than a threshold such that a relearnprocess is enabled) at block 526. When all of these enable conditionsare satisfied at block 527, a trigger signal is output to the EGR pickuplong term adaptation block 522. Parameters utilized in the EGR pickuplong term adaptation block 522 include exhaust mass flow 528, measuredpressures 529 from sensors 160, 162, barometric pressure 530, and an EGRpickup to barometric pressure loss (P-Loss) table 531. An EGR pickupadaptation weight factor block 532 calculates and outputs an EGR pickupadaptation weight factor based on the exhaust mass flow 528. In oneexemplary implementation, higher exhaust gas pressures are given ahigher weight factor as they are considered more reliable.

A difference block 533 calculates and outputs a difference between themeasured exhaust gas and barometric pressures 529, 530. Block 534calculates a ratio or quotient of the output of block 533 and the EGRpickup to barometric pressure loss from table 531. The output of block534 is multiplied by the EGR pickup adaptation weight factor (from block532) at block 535 to obtain an EGR pickup pressure multiplier. The EGRpickup adaptation weight factor is also accumulated at block 536 whilethe trigger signal is output from the enable conditions block 521.Similarly, the EGR pickup pressure multiplier is also accumulated atblock 537 while the trigger signal is output from the enable conditionsblock 521. When the quantity of accumulation exceeds a threshold (e.g.,a minimum number of samples), block 538 calculates and outputs a ratioor quotient of the accumulated EGR pickup adaptation weight factor andthe accumulated EGR pickup pressure multiplier. The output of block 538is the final EGR pickup pressure multiplier. Provided this final EGRpickup pressure multiplier results in the modeled EGR pickup pressurebeing within an accuracy or error threshold, the EGR pickup long termadaptation is complete. Alternatively, if the requisite accuracy is notachieved, the EGR pickup pressure learn complete flag remains false andthe learning process continues. For example, this flag could be flippedfrom true to false when the system changes and the modeled pressurebecomes inaccurate (e.g., exceeding a threshold), and thus a relearnprocess would be enabled.

FIG. 5C illustrates an example architecture 540 for the EGR coolerpressure long term adaptation block 502. The architecture 540 isgenerally divided into enable conditions block 541 and the actual EGRcooler long term adaption block 542. The enable conditions 541 blockincludes EGR mass flow being above a certain threshold at block 543, theexhaust and EGR mass flows being stable (e.g., remaining within certainranges) at block 544, the EGR valve delta pressure and dP valve outletpressure sensors 160, 162 being ready for measurement (e.g., nofaults/malfunctions) at block 545, the EGR pickup pressure learn flagbeing true (see FIG. 5B and above) at block 546, and the EGR coolerpressure learn complete flag being false (e.g., a learn has not alreadybeen performed or the modeled pressure is larger than a threshold suchthat a relearn process is enabled) at block 547. When all of theseenable conditions are satisfied at block 548, a trigger signal is outputto the EGR cooler long term adaptation block 542. Parameters utilized inthe EGR cooler long term adaptation block 542 include EGR mass flow 549,measured pressures 550 from sensors 160, 162, the modeled EGR pickuppressure 551, and an EGR cooler loss table 552. An EGR cooler adaptationweight factor block 553 calculates and outputs an EGR cooler adaptationweight factor based on the EGR mass flow 549. In one exemplaryimplementation, higher EGR pressures are given a higher weight factor asthey are considered more reliable. A difference block 554 calculates andoutputs a difference between the measured EGR valve inlet and modeledEGR pickup pressures 550, 551.

Block 555 calculates a ratio or quotient of the output of block 554 andthe EGR cooler pressure loss from table 552. The output of block 555 ismultiplied by the EGR cooler adaptation weight factor (from block 553)at block 556 to obtain an EGR cooler pressure multiplier. The EGR cooleradaptation weight factor is also accumulated at block 557 while thetrigger signal is output from the enable conditions block 541.Similarly, the EGR cooler pressure multiplier is also accumulated atblock 558 while the trigger signal is output from the enable conditionsblock 541. When the quantity of accumulation exceeds a threshold (e.g.,a minimum number of samples), block 559 calculates and outputs a ratioor quotient of the accumulated EGR cooler adaptation weight factor andthe accumulated EGR cooler pressure multiplier. The output of block 559is the final EGR cooler pressure multiplier. Provided this final EGRcooler pressure multiplier results in the modeled EGR cooler pressurebeing within an accuracy or error threshold, the EGR cooler long termadaptation is complete. Alternatively, if the requisite accuracy is notachieved, the EGR cooler pressure learn complete flag remains false andthe learning process continues. For example, this flag could be flippedfrom true to false when the system changes and the modeled pressurebecomes inaccurate (e.g., exceeding a threshold), and thus a relearnprocess would be enabled.

FIG. 5D illustrates an example architecture 570 for the air filterpressure loss long term adaptation block 503. The architecture 570 isgenerally divided into enable conditions block 571 and the actual airfilter long term adaption block 572. The enable conditions 571 blockincludes the dP valve 110 being effective/open (e.g., not closed ormalfunctioning) at block 573, the air mass flow being stable (e.g.,remaining within a certain range) at block 574, the dP valve outletpressure sensors 162 being ready for measurement (e.g., nofaults/malfunctions) at block 575, and the air filter pressure learncomplete flag being false (e.g., a learn has not already been performedor the modeled pressure is larger than a threshold such that a relearnprocess is enabled) at block 576. When all of these enable conditionsare satisfied at block 577, a trigger signal is output to the air filterlong term adaptation block 572. Parameters utilized in the air filterlong term adaptation block 572 include air mass flow 578, barometricpressure 579, measured pressure 580 from sensor 162, dP valve pressureloss 581, and an air filter pressure loss table 582. An air filteradaptation weight factor block 583 calculates and outputs an air filteradaptation weight factor based on the air mass flow 578. In oneexemplary implementation, higher EGR pressures are given a higher weightfactor as they are considered more reliable. A difference block 584calculates and outputs a difference between the barometric pressure 579and the measured air pressure and dP valve pressure loss 580, 581.

Block 585 calculates a ratio or quotient of the output of block 584 andthe air filter pressure loss from table 582. The output of block 585 ismultiplied by the air filter adaptation weight factor (from block 583)at block 586 to obtain an air filter pressure multiplier. The air filteradaptation weight factor is also accumulated at block 587 while thetrigger signal is output from the enable conditions block 571.Similarly, the air filter pressure multiplier is also accumulated atblock 588 while the trigger signal is output from the enable conditionsblock 571. When the quantity of accumulation exceeds a threshold (e.g.,a minimum number of samples), block 589 calculates and outputs a ratioor quotient of the accumulated air filter adaptation weight factor andthe accumulated air filter pressure multiplier. The output of block 589is the final air filter pressure multiplier. Provided this final airfilter pressure multiplier results in the modeled air filter outletpressure being within an accuracy or error threshold, the air filterlong term adaptation is complete. Alternatively, if the requisiteaccuracy is not achieved, the air filter pressure learn complete flagremains false and the learning process continues. For example, this flagcould be flipped from true to false when the system changes and themodeled pressure becomes inaccurate (e.g., exceeding a threshold), andthus a relearn process would be enabled.

FIG. 5E illustrates an example architecture 600 for the EGR valve inletpressure short term adaptation block 504. A difference is calculatedbetween the measured and modeled EGR valve inlet pressures 601, 602 atblock 603. This difference is filtered to remove noise and a filtereddifference is output by block 605. If an EGR cooler adaptation learningis initiated, however, block 604 triggers a reset or temporary disablefor the filter block 605. A latch 607 is enabled when both the EGR valvedelta pressure and dP valve outlet pressure sensors 160, 162 are ready(e.g., no faults or malfunctions) per block 606. When enabled, the latch607 passes the filtered difference as a short term correction value forthe EGR valve inlet pressure. This filtered difference is also stored inmemory 608. When the latch 607 is disabled (e.g., one of the sensors160, 162 is not ready), the stored filtered difference is retrieved andpassed by the latch 607 as the short term correction value for the EGRvalve inlet pressure. The EGR mass flow 609 is also filtered to removenoise by filter block 610. Filter block 610 is similarly reset/disabledwhen the EGR cooler adaptation learning is initiated. Another latch 612is enabled when both the sensors 160, 162 are ready per block 611. Whenenabled, the latch 612 passes the filtered EGR mass flow to block 614,which is also stored in memory 613. When the latch 612 is disabled, thestored filtered EGR mass flow is retrieved and passed by the latch 612to block 614. Block 614 calculates a quotient or ratio of the filtereddifference and the filtered EGR mass flow to obtain a short termmultiplier for the EGR valve inlet pressure.

FIG. 5F illustrates an example architecture 620 for the dP valve outletpressure short term adaptation block 505. A difference is calculatedbetween the measured and modeled dP valve outlet pressures 621, 622 atblock 623. This difference is filtered to remove noise at block 625. Ifan air filter adaptation learn is initiated, however, block 624 triggersa reset or temporary disable for the filter block 625. A latch 627 isenabled when the dP valve outlet pressure sensors 160 is ready (e.g., nofaults or malfunctions) per block 626. When enabled, the latch 627passes the filtered difference as a short term correction value for thedP valve outlet pressure. This filtered difference is also stored inmemory 628. When the latch 627 is disabled (e.g., sensor 162 is notready), the stored filtered difference is retrieved and passed by thelatch 627 as the short term correction value for the dP valve outletpressure.

Referring now to FIGS. 6A-6B, flow diagrams of example methods 640, 680of gas pressure adaptation is illustrated. It will be appreciated thatthese methods 640 could be executed or performed by the controller 156simultaneously, partially overlapping, or entirely separately.

FIG. 6A illustrates a first example gas pressure adaptation method 640.At 642, the controller 156 receives the measured EGR valve deltapressure and the measured dP valve outlet pressure. At 644, thecontroller 156 determines whether the EGR pickup adaptation learning iscomplete. If true, the method 640 proceeds to 654. If false, thecontroller 156 determines whether the EGR pickup adaptation learning isenabled. If true, the method proceeds to 648. If false, the method 640ends or returns to 642. At 648, the controller 156 performs the EGRpickup to barometric pressure loss learning until the learning iscomplete at 650. When the learning is complete, the EGR pickupadaptation multiplier is learned and used by the controller 156 at 652and the method 640 ends or returns to 642 (e.g., to learn the EGR cooleradaptation). At 654, the controller 156 determines whether the EGRcooler adaptation learning is enabled. If true, the method 640 proceedsto 656. If false, the method 640 ends or returns to 642. At 656, thecontroller performs the EGR cooler pressure loss learning until thelearning is complete at 658. When the learning is complete, the EGRcooler adaptation multiplier is learned and used by the controller 156at 660 and the method 640 ends or returns to 642.

FIG. 6B illustrates a second example gas pressure adaptation method 680.At 682, the controller 156 receives the measured dP valve outletpressure. At 684, the controller 156 determines whether the air filterloss adaptation learning is enabled. If true, the method 680 proceeds to686. If false, the method 680 ends or returns to 682. At 686, thecontroller 156 performs the air filter loss adaption learning until thelearning is complete at 688. When the learning is complete, the airfilter adaptation multiplier is learned and used by the controller 156at 690 and the method 680 ends or returns to 680.

Exhaust Gas Constituent Tracking

Referring now to FIGS. 7A-7B, diagrams of example exhaust gasconstituent tracking features are illustrated. In one exemplaryimplementation, at least a portions of the architecture of FIG. 7B isimplemented in the controller 156.

FIG. 7A illustrates an entire flow path 700 of EGR from the exhaust gasconcentration sensor 164 b to cylinders/an intake port of the engine102. This flow path 700 includes a number of components. For example,these components could include the EGR cooler 154, the EGR valve 154,the compressor 116, the charge air cooler (CAC) 124, the throttle valve122, and the intake manifold 126. In order to accurately track exhaustgas constituents (e.g., air, unburned mixture, inert gas, etc.), eachportion of the flow path must be accurately modeled. These exhaust gasconstituents can be calculated, for example, based on the FA of theexhaust gas. The flow path is generally divided into nine distinctregions: (1) region 701 from the exhaust gas concentration sensor 164 b(e.g., a WRO2 sensor) to the EGR pickup point, (2) region 702 from theEGR pickup point to an inlet of the EGR cooler 154, (3) region 703 fromthe inlet of the EGR cooler 154 to an outlet of the EGR cooler 154, (4)region 704 from the outlet of the EGR cooler across the EGR valve 150and to the EGR port or mixing point with air in the induction pipe 112,(5) region 705 from the EGR port to an inlet of the compressor(s) 116,(6) region 706 from the outlets of the compressor(s) 116 to the inlet ofthe CAC 124, (7) region 707 from the inlet of the CAC 124 to an outletof the CAC 124, (8) region 708 from the outlet of the CAC 124 to aninlet of the throttle valve 122, and (9) region 709 from an outlet ofthe throttle valve 122 across the intake manifold 126 to thecylinders/intake port of the engine 102.

FIG. 7B illustrates an example architecture 720 for modeling the flowpath 700 to accurately track the exhaust gas constituents throughout theflow path 700. More specifically, this architecture illustrates modelassumptions regarding whether certain components are assumed to affectEGR mass and/or EGR density. In region 701 from the exhaust gasconcentration sensor 164 b, there is a constant exhaust gas density.However, at the EGR pickup point 721, there is a change in mass as notall of the exhaust gas is recirculated via the LPEGR system 146. Thecontroller 156 accounts for this mass change. From the EGR pickup point721 to the inlet of the EGR cooler 154, there is constant EGR density.However, across the EGR cooler 154, there is a change in EGR densitythat is accounted for by the controller 156. From the outlet of the EGRcooler 154 across the EGR valve 150 and to the EGR port or mixing point722, there again is a constant density. However, at the EGR port ormixing point 722, there is a change in mass as the EGR is combined withair from the induction pipe(s) 112. The controller accounts for thismass change. From the EGR port 722 to a compressor inlet point 723,there is constant density. However, there is a density change across thecompressor(s) 116 that is accounted for by the controller 156. From thecompressor outlet point, there is constant density until the CAC inletpoint. There are also flow dynamics from the compressor(s) 116 all theway to the CAC 124 to be accounted for by the controller 156. There isanother density change from the CAC inlet point 724 and across the CAC124 that is accounted for by the controller 156. While there is aconstant density from the CAC 124 to the throttle valve 122 (orvice-versa), there is another density change from a throttle valve inletpoint 725 and across the throttle valve 122, but there is constantdensity from the outlet of the throttle valve 122 and across the intakemanifold 126 to the cylinder port or intake point of the engine 102.Again, the controller 156 accounts for flow dynamics through the intakemanifold.

Referring now to FIGS. 7C-7D, example buffering features utilized by thecontroller 156 in performing the exhaust gas constituent tracking areillustrated. As discussed above and shown in FIG. 7C, changes in exhaustgas/EGR mass and density affect how exhaust gas constituents should betracked. Each of the portions 701-709 of the flow path 700 can bemodeled using a buffer 740 comprising a plurality of cells 742-1 . . .742-N (N=8 as shown). A total size 744 of the buffer 742 equals a sizeof each cell 742 times N. Each cell represents a portion of a particularpath portion and the exhaust gas/EGR mass is able to be calculated basedon the known hardware configuration and other parameters (temperature,pressure, volume, etc.). For example, the mass for a particular cellcould be calculated by dividing (i) a product of the pressure (P) andvolume (V) for the particular cell by (i) a produce of a gas constant(R) and the temperature (T) for the particular cell). Partial cells 748can also be utilized as shown by incoming mass 746. These partial cells748, however, may be loaded into the buffer 740 last (e.g., after theother three cells of incoming mass 746).

As shown in FIG. 70, density changes affect buffer operation. Whenexpansion/density decreases (flow out<flow in, e.g., at throttletip-in), a portion of the exhaust gas/EGR mass is pushed out of the pathportion. As shown, buffer 760 a includes six cells 1-6. After a 50%expansion or density reduction, the data in the last three cells 4-6 ispushed out of the buffer (e.g., to a next buffer for a subsequent pathportion) due to the decreased density and the remaining data in thefirst three cells 1-3 is spread across all six cells 1-6 as shown at 760b. The remaining exhaust gas/EGR mass is then divided across the buffercells for that path portion. Conversely, when compression/densityincreases (flow in>flow out, e.g., at throttle tip-out), the exhaustgas/EGR mass is stored in a latter portion of the buffer cells and theformer buffer cells are freed up to account for the incoming exhaustgas/EGR mass. As shown, buffer 780 a includes six cells 1-6. After a 50%compression or density increase, the data in the six cells 1-6 isconsolidated across the last three cells 4-6 (e.g., in six half-sized orpartial cells) to make room in cells 1-3 for incoming exhaust gas/EGRcaused by the increase density as shown at 780 b. It will be appreciatedthat the 50% density changes illustrated and discussed above areexamples values and the buffers could be manipulated in response to anysuitable density changes.

Referring now to FIG. 8, a flow diagram of an example method 800 ofexhaust gas constituent tracking through the LPEGR system 146 and theinduction system 104 of the turbocharged engine 102 is illustrated. At804, the controller 156 receives a measured exhaust air/fuel ratio (FA)or lambda. At 808, the controller 156 calculates the lambda at the EGRpickup point. At 812, the controller 156 calculates the lambda at theEGR cooler inlet point. At 816, the controller 156 calculates the lambdaat the EGR cooler outlet point. At 820, the controller 156 calculatesthe EGR fraction and EGR fuel at the EGR port or mixing point. At 824,the controller 156 calculates the EGR fraction and EGR fuel at thecompressor inlet point(s). These values are utilized by the controller156 for turbocharger (e.g., wastegate valve) control. At 826, thecontroller 156 calculates the EGR fraction and EGR fuel at the throttlevalve inlet point. These values are utilized by the controller 156 tocontrol the throttle valve 122. At 832, the controller 156 calculatesthe EGR fraction and EGR fuel at the cylinder port or intake port of theengine 102. These values are utilized by the controller 156 inconnection with an EGR check procedure in connection with engineshutdown and restart operations (e.g., accounting for any residual EGRin the intake manifold 126 during shutdown/restart). The method 800 thenends or returns to 804.

While the gas constituent tracking techniques discussed herein aredescribed with respect to tracking exhaust gas constituents through anLPEGR system and an induction system of a turbocharged engine, it willbe appreciated that these techniques could be applied to any systemhaving a long gas flow path such that the gas constituents must beaccurately tracked throughout the gas flow path to achieve precisesystem control.

It should also be understood that the mixing and matching of features,elements, methodologies and/or functions between various examples may beexpressly contemplated herein so that one skilled in the art wouldappreciate from the present teachings that features, elements and/orfunctions of one example may be incorporated into another example asappropriate, unless described otherwise above.

What is claimed is:
 1. A control system for a vehicle including agasoline engine, a turbocharger comprising a wastegate valve, and a lowpressure exhaust gas recirculation (LPEGR) system, the LPEGR systemcomprising an EGR cooler and an EGR valve downstream from the EGRcooler, the LPEGR system being configured to recirculate exhaust gasproduced by the engine from an exhaust system of the engine to aninduction system of the engine, the control system comprising: athrottle valve disposed in the induction system between a compressor ofthe turbocharger and an intake port of a cylinder of the engine andconfigured to control airflow into the engine; a fuel injectorconfigured to inject gasoline into the cylinder; a spark plug configuredto generate a spark to ignite a mixture of gas and the gasoline withinthe cylinder; an exhaust gas concentration sensor upstream from an EGRpickup of the LPEGR system and configured to measure an air/fuel ratioof the exhaust gas; and a controller configured to: receive a measuredair/fuel ratio of the exhaust gas from the exhaust gas concentrationsensor; determine an air/fuel ratio of the exhaust gas at the EGR pickuppoint; determine an air/fuel ratio of the exhaust gas at an inlet of theEGR cooler; determine an air/fuel ratio of the exhaust gas at an outletof the EGR cooler; determine a first exhaust gas fraction and a firstfuel fraction at an EGR port upstream from the compressor in theinduction system where the exhaust gas mixes with air; determine a setof second exhaust gas fractions and second fuel fractions at a set ofrespective points in the induction system downstream from the EGR port;and control at least one of the wastegate valve, the throttle valve, thefuel injector, and the spark plug based on the set of second exhaust gasfractions and second fuel fractions to prevent misfires of the engine.2. The control system of claim 1, wherein the controller is configuredto control the wastegate valve based on a determined second exhaust gasfraction and a determined second fuel fraction at an inlet of thecompressor.
 3. The control system of claim 2, wherein the controller isconfigured to control the throttle valve based on a determined secondexhaust gas fraction and a determined second fuel fraction at an inletof the throttle valve.
 4. The control system of claim 3, wherein thecontroller is configured to control the fuel injector and the spark plugbased on a determined second exhaust gas fraction and a determinedsecond exhaust gas fraction at the cylinder intake port.
 5. The controlsystem of claim 4, wherein the controller is further configured toutilize the determined second exhaust gas fraction and the determinedsecond exhaust gas fraction at the cylinder intake port as part of anEGR condition check upon shutdown and restart of the engine.
 6. Thecontrol system of claim 1, wherein the induction system furthercomprises a differential pressure (dP) valve disposed upstream of theEGR port and downstream from an air filter of the induction system. 7.The control system of claim 6, wherein the controller determines theexhaust gas fraction and fuel fraction at the EGR mixing point based onthe operation of the dP valve.
 8. The control system of claim 1, whereinthe controller is configured to divide a flow path of the exhaust gasthrough the LPEGR system and the induction system into the followingdistinct portions: (i) a first portion from the exhaust gasconcentration sensor to the EGR pickup point; (ii) a second portion fromthe EGR pickup point to the EGR cooler inlet; (iii) a third portion fromthe EGR cooler inlet across the EGR cooler to the EGR cooler outlet;(iv) a fourth portion from the EGR cooler outlet across the EGR valve tothe EGR port; (v) a fifth portion from the EGR port to the compressorinlet; (vi) a sixth portion from an outlet of the compressor to an inletof a cold air cooler of the induction system; (vii) a seventh portionacross the cold air cooler; (viii) an eighth portion from an outlet ofthe cold air cooler to an inlet of the throttle valve; and (ix) a ninthportion from an outlet of the throttle valve across an intake manifoldof the induction system to the cylinder intake port.
 9. The controlsystem of claim 8, wherein the controller utilizes predeterminedinformation about the configuration of the LPEGR system and theinduction system and distinct memory buffers to track (i) the air/fuelratio of the exhaust gas between the nine distinct portions of the flowpath before EGR mixing and (ii) EGR/fuel fractions between the ninedistinct potions of the flow path after EGR mixing.
 10. The controlsystem of claim 9, wherein the controller is configured to vary air/fuelratio data or EGR/fuel fraction data stored in each memory buffer toaccount for (i) mass changes at the EGR pickup point and the EGR port,(ii) density changes in across the EGR cooler, the compressor, the coldair cooler, and the throttle valve, and (iii) dynamic flows from anoutlet of the compressor to the inlet of the cold air cooler and from anoutlet of the throttle valve to the cylinder intake port.
 11. A methodfor tracking exhaust gas constituents for a vehicle including a gasolineengine having a turbocharger with a wastegate valve, a throttle valvedisposed in an induction system between a compressor of the turbochargerand an intake port of a cylinder, a fuel injector configured to injectgasoline into the cylinder, and a spark configured to generate sparkwithin the cylinder, the vehicle further including a low pressureexhaust gas recirculation (LPEGR) system having an EGR cooler and an EGRvalve and being configured to recirculate exhaust gas produced by theengine from an exhaust system to the induction system, the methodcomprising: receiving, by a controller and from an exhaust gasconcentration sensor upstream from an EGR pickup point of the LPEGRsystem, a measured air/fuel ratio of the exhaust gas; determining, bythe controller, an air/fuel ratio of the exhaust gas at the EGR pickuppoint; determining, by the controller, an air/fuel ratio of the exhaustgas at an inlet of the EGR cooler; determining, by the controller, anair/fuel ratio of the exhaust gas at an outlet of the EGR cooler;determining, by the controller, a first exhaust gas fraction and a firstfuel fraction at an EGR port upstream from the compressor in theinduction system where the exhaust gas mixes with air; determining, bythe controller, a set of second exhaust gas fractions and second fuelfractions at a set of respective points in the induction systemdownstream from the EGR port; and controlling, by the controller, atleast one of the wastegate valve, the throttle valve, the fuel injector,and the spark plug based on the set of second exhaust gas fractions andsecond fuel fractions to prevent misfires of the engine.
 12. The methodof claim 11, further comprising controlling, by the controller, thewastegate valve based on a determined second exhaust gas fraction and adetermined second fuel fraction at an inlet of the compressor.
 13. Themethod of claim 12, further comprising controlling, by the controller,the throttle valve based on a determined second exhaust gas fraction anda determined second fuel fraction at an inlet of the throttle valve. 14.The method of claim 13, further comprising controlling, by thecontroller, the fuel injector and the spark plug based on a determinedsecond exhaust gas fraction and a determined second exhaust gas fractionat the cylinder intake port.
 15. The method of claim 14, furthercomprising utilizing, by the controller, the determined second exhaustgas fraction and the determined second exhaust gas fraction at thecylinder intake port as part of an EGR condition check upon shutdown andrestart of the engine.
 16. The method of claim 11, wherein the inductionsystem further comprises a differential pressure (dP) valve disposedupstream of the EGR port and downstream from an air filter of theinduction system.
 17. The method of claim 16, further comprisingdetermining, by the controller, the exhaust gas fraction and fuelfraction at the EGR mixing point based on the operation of the dP valve.18. The method of claim 11, further comprising dividing, by thecontroller, a flow path of the exhaust gas through the LPEGR system andthe induction system into the following distinct portions: (i) a firstportion from the exhaust gas concentration sensor to the EGR pickuppoint; (ii) a second portion from the EGR pickup point to the EGR coolerinlet; (iii) a third portion from the EGR cooler inlet across the EGRcooler to the EGR cooler outlet; (iv) a fourth portion from the EGRcooler outlet across the EGR valve to the EGR port; (v) a fifth portionfrom the EGR port to the compressor inlet; (vi) a sixth portion from anoutlet of the compressor to an inlet of a cold air cooler of theinduction system; (vii) a seventh portion across the cold air cooler;(viii) an eighth portion from an outlet of the cold air cooler to aninlet of the throttle valve; and (ix) a ninth portion from an outlet ofthe throttle valve across an intake manifold of the induction system tothe cylinder intake port.
 19. The method of claim 18, further comprisingutilizing, by the controller, predetermined information about theconfiguration of the LPEGR system and the induction system and distinctmemory buffers to track (i) the air/fuel ratio of the exhaust gasbetween the nine distinct portions of the flow path before EGR mixingand (ii) the EGR/fuel fractions between the nine distinct portions ofthe flow path after EGR mixing.
 20. The method of claim 19, furthercomprising varying, by the controller, air/fuel ratio data or theEGR/fuel fraction data stored in each memory buffer to account for (i)mass changes at the EGR pickup point and the EGR port, (ii) densitychanges in across the EGR cooler, the compressor, the cold air cooler,and the throttle valve, and (iii) dynamic flows from an outlet of thecompressor to the inlet of the cold air cooler and from an outlet of thethrottle valve to the cylinder intake port.